DESCRIPTION Membrane trafficking and microtubule transport are essential to the development and maintenance of neuronal polarity. The primary facilitators of microtubule-dependent transport are the microtubule-motors kinesin and cytoplasmic dynein. These motor proteins function complexed with regulatory accessory factors. The investigators have identified several critical components of these complexes involved in membrane trafficking. These components include kinesin, dynactin and kinectin. The applicants' current working model defines the vesicle-bound motor receptor as playing a central role in organelle transport. Kinectin is the only motor receptor identified to date. Initially kinectin was described as a receptor for kinesin. However, evidence that kinectin will also bind cytoplasmic dynein led them to postulate that kinectin is the major motor receptor and that modification of kinectin can switch it from an anterograde-motor receptor to a retrograde-motor receptor. They have identified several enzymes that are capable of modifying kinectin and other members of the motility-complex. These enzymes include kinases, phosphatases and the small G proteins, rac1 and rhoA. While it is clear that these factors affect regulation of motility, their precise interactions and control mechanisms are not yet known. To understand the molecular basis of motor-complex mediated trafficking in neurons, the applicants plan to do the following: identify additional protein components of the organelle-motor complex (focusing on motor receptors); prepare probes and reagents to alter the functions of these specific proteins and kinectin; use in vitro motility assays to define the roles of these proteins (kinectin) in the direction, the velocity and the level of organelle motility; examine the roles of these proteins (kinectin) in the steps of viral glycoprotein export and endocytic membrane trafficking in neuronal axons and dendrites; and determine the structure of the kinectin-kinesin and the kinectin-rhoA GTPase complexes at the atomic level.